Another capability of the invention uses low-impact springs to reduce the maximum impact force felt by the runner. These optimal springs can be used both in high-performance energy return shoes and in conventional shoes. With reference to FIGS. 1-3, the goal of the alternative design of FIGS. 28-30 is to make more robust the capability to achieve an optimal force curve (which requires that the force curve bend over during the compression of the shoe sole). This is achieved with a modification of how the spreading linkage is connected to the curved spring. The details of the revised linkage-to-curved spring hinges, the construction of the linkage, and curved spring itself are shown in FIG. 31. With reference to FIGS. 13 and 15, the goal of the alternative design of FIG. 32 of the invention of the instant provisional patent is to load the ring spring only by spreading it at its sides. The details of the construction of this linkage and this spring are also shown in FIG. 32. Notably, the tied cogged hinge of FIG. 47 can be used for the corner hinges of the parallelogram of FIGS. 7-9, for the internal linkage hinges of FIGS. 13, 15 and 32, and for the rotating arms joint of FIGS. 27 and 49.
The goal of the design of the merging arms embodiment of FIGS. 33-36 of the instant provisional application is to modify the ring spring of FIG. 32 in such a manner that it becomes both stronger and tougher, whereby the term tougher means that the new ring spring is capable of absorbing significantly more energy before breaking. This goal is accomplished by making the outer arms slightly bowed out and longer—in such a way that they just merge at full ring spring compression. There are also two types of improvements of the pivots. The first kind features enhanced novel necked down natural hinges which address the issue of composite brittleness with more flexible matrix materials. The second kind features tied cogged hinges which do not utilize natural hinges, but which can still be inexpensively manufactured—even at the small linkage sizes required in the shoe. This design is called the merging arms internal linkage ring spring. A variation of this design is called the overlaid merging laminates beam, in which sinusoidal-like, out-of-phase, adjacent laminates merge as the beam is bent. For both of these designs, there results a much tougher, much stronger merged structure than if you just added two independent laminates. This is because the merged laminate structure transitions to a cohesive structure twice as thick, and the spring strength goes as the cube of the thickness. If the comparison is for the case of two merged laminates, there is a benefit of two squared (a factor of four) in strength per weight. As the number of laminates increases, this benefit goes as the number of laminates squared. Also, since the bulged out laminates, e.g., are absorbing more energy by flexing more, these structures are much tougher.
Also, optimal performance requires a large sole compression for all impact forces (running speeds). The first gear change mechanism herein of FIG. 26 automatically changes the spring system stiffness so that there is always close to full sole compression. Additional simplified designs for gear change are shown in FIGS. 37-44 and in FIGS. 46 and 48. These include versions that are strictly mechanical or that also use electronic actuators. Notably, there are designs for precise gear change over a continuous range, not just at a few discrete gear levels like with a bike or a car. More notably, the cross synchronized pulley actuated automatic gear changer of FIG. 48 synchronizes the gear change of the inside assembly with that of the inside assembly in a manner that is optimally simple and easy to manufacture. Also, the precision of the gear change (equivalent to the number of gears) can be improved to the point where it is equivalent to the theoretically completely precise gear change of FIGS. 37 and 38. There are also designs for novel shoe impact electric chargers—both for the enhanced heel-lift shoe with large heel travel, and for a clip-on design for all shoes. These chargers are cheaper than those of the prior art, and they provide far more electric power. There is also a novel pulley actuator which is lighter, cheaper, simpler, and faster than those of that prior art. Finally, the optimal low-impact springs herein are improved so that they are significantly tougher and stronger. The sum of all these capabilities is a futuristic running/walking shoe with 40% lower impact force springs and with approximately 20% energy return at all walking/running speeds—by virtue of the fact that the effective spring strength (gear) is automatically changed step by step with a automatic gear changer which is powered by a shoe impact charger. There is also a variation of optimal springs for limbs rotating about a joint. Combining this with the electronic gear changer herein leads to a light, inexpensive energy return knee brace. It is conceivable that each of these two enhancements (the smart energy return shoe knee brace) can provide a 25% reduction in the metabolic energy cost of running. Thus, their combined energy return can be 50%.